Polycyclic Aromatic Hydrocarbons in Bivalves From Mangrove Ecosystems Affected by the 2019 Brazilian Oil Spill

Abstract The 2019 oil spill along the Brazilian coast affected extensive mangrove ecosystems and raised concerns regarding hydrocarbon contamination in seafood resources. This study evaluated the accumulation of polycyclic aromatic hydrocarbons (PAHs) in marine bivalves collected from mangrove areas along the Bahia coast, including oil-spill-affected sites, a chronically contaminated estuary (São Paulo River), and a reference area (Itacaré). Crassostrea rhizophorae, Mytella charruana, and Anomalocardia flexuosa were sampled during two campaigns (August–September 2020 and February–April 2021), and PAHs were quantified by gas chromatography–mass spectrometry. Total PAH concentrations ranged from 25.9 to 537 ng g⁻¹ dry weight. Spatial differences were evident, with higher concentrations generally observed in Belmonte and the São Paulo River and lower levels at the reference site. Significant differences among species were detected (one-way ANOVA, p = 0.009), with M. charruana exhibiting the highest concentrations, which may be related to its closer association with fine, organic-rich sediments that favor PAHs retention. No significant temporal variation was observed between sampling campaigns (two-way ANOVA, p = 0.765),suggesting continued exposure to PAHs after the spill period. Multivariate analysis revealed distinct compositional patterns among sites and indicated the influence of multiple contamination sources. The results support a multifactorial contamination scenario involving residual oil-derived inputs, pre-existing contamination, and ongoing diffuse anthropogenic sources. Incremental Lifetime Cancer Risk (ILCR) assessment indicated negligible to low carcinogenic risk for most samples under short- and medium-term exposure scenarios, whereas potential risk was restricted to a small number of samples from Belmonte and the São Paulo River under long-term exposure conditions. Non-carcinogenic risk remained negligible for all evaluated compounds. These findings demonstrate that contamination patterns in tropical estuaries affected by oil spills may be strongly influenced by pre-existing chronic pollution, complicating the assessment of environmental recovery and seafood safety